RU2695775C1 - Method of measuring margin by osnr in communication line with spectral multiplexing dwdm and encoding signal with fec error correction - Google Patents

Abstract

FIELD: optics.

SUBSTANCE: invention relates to fibre-optic communication, particularly to efficiency estimation in fiber-optic communication lines, and more specifically to OSNR margin measurement procedure in communication line with DWDM spectral multiplexing and FEC error correction signal coding. For this, in OSNR margin measurement method, including following stages: before putting communication line into operation OSNR_BTB value is measured and OSNR dependence from BER in circuit with test short line without FEC errors correction, during communication line putting into operation OSNR_OSA1 value is measured at communication line end, during operation periodical measurements of communication line parameters are made, based on the values of which taking into account the values of parameters measured before putting the communication line into operation, the reserve OSNR_M by OSNR, OSNR dependence on BER is presented in the form of polynomial of second degree: OSNR=a ₀+a ₁log(BER)+a ₂ (log(BER)²), where a ₀, a ₁ and a ₂ - second-degree polynomial coefficients approximating the experimentally measured dependence of OSNR on BER in the test line, when the communication line is put into operation on its section until FEC errors are corrected, measuring the error coefficient BER1, during operation of a communication line on its section until FEC errors are corrected, mean value of error coefficient BER2 is measured periodically and value OSNR_M is calculated from value of measured values by OSNR.

EFFECT: technical result consists in simplification of OSNR margin measurement in communication line with spectral seal.

1 cl, 1 tbl, 2 dwg

Description

The invention relates to the field of fiber optic communication, in particular to the evaluation of efficiency in fiber optic communication lines, and more particularly to a procedure for measuring OSNR margin in a communication line with DWDM spectral multiplexing and FEC error correction signal coding using noise loading.

The prior art method for measuring OSNR margin in a communication line using a noise load, which is based on measuring the dependence of OSNR on the Q-factor using a noise load, measuring BER and converting its value to the Q factor by a certain formula and calculating the margin OSNR based on the data obtained (Patent EP 0903874, publ. 24.03.1999).

The disadvantages of the known technical solution include the impossibility of taking measurements without interrupting the operation of the communication system, due to the need to disconnect the information signal from the consumer during measurements and apply it to the optical spectrum analyzer (OSA) to determine the value of the OSNR line and the need to supply additional noise load during measurements into the communication line to determine the magnitude of the required OSNR line.

The closest to the claimed prototype is a method for measuring OSNR margin in a communication line with DWDM spectral multiplexing and FEC error correction signal coding, which includes the following steps: before commissioning the communication line, the OSNR _BTB value and the OSNR dependence on BER are measured in the circuit a short line test without correction FEC error during link commissioning OSNR _OSA1 value measured at the end of the link, in the operation carried out periodic measurements of link parameters according to the value oryh with the parameter values measured before the link commissioning, calculated margin osnr _M of OSNR (OSNR System Margin Estimation by Nonlinear Noise Insensitive OSNR Monitor, Tomohiro Yamauchi, Shoichiro Oda, Liang Dou, Xiaofei Su, Takeshi Hoshida, Yasuhiko Aoki, Zhenning Tao, and Jens C. Rasmussen, ECOC 2016 42nd European Conference and Exhibition on Optical Communications ⋅ September 18-22, 2016 ⋅ Dusseldorf, p. 277-279).

Unlike the analogue, the prototype allows you to reduce the number of measurements required to calculate the OSNR margin taken during the operation of the DWDM communication system. In the prototype, it is not necessary during measurements to provide additional noise load to the communication line to determine the magnitude of the required OSNR line.

The disadvantages of the prototype (as well as the analogue) include the impossibility of taking measurements without interrupting the operation of the communication system, due to the need to disconnect the information signal from the consumer during measurements and apply it to the optical spectrum analyzer (OSA) to determine the value of the OSNR line. This does not allow constant monitoring of the quality of work of all DWDM channels of the communication system directly during operation.

The objective of the invention is to provide a simple and reliable method for measuring OSNR margin in a communication line with spectral multiplexing, which does not require disconnecting the information signal from the consumer during measurements.

EFFECT: simplification of OSNR margin measurement in a communication line with spectral multiplexing due to the possibility of continuous monitoring of the quality of operation of all DWDM communication system channels directly during operation without interruption for the duration of measurements.

оптимально усреднение значения BER2 производить в течение не менее 10 минут.The problem is solved, and the claimed technical result is achieved by the fact that in the method of measuring OSNR margin in a communication line with DWDM spectral multiplexing and FEC error correction signal coding, which includes the following steps: before commissioning the communication line, the OSNR _BTB value and the dependence are measured BER OSNR in a circuit with a test short line without correction of FEC errors; during commissioning of the communication line, the OSNR _{OSA1 value} at the end of the communication line is measured; during operation, periodic measurements of pairs communication line meters, the value of which, taking into account the values of the parameters measured before putting the communication line into operation, calculates the osnr _M supply by OSNR, the OSNR dependence on BER is represented as a polynomial of the second degree: OSNR = a ₀ + a ₁ log (BER) + a ₂ (log (BER)) ² , where a ₀ , a ₁ and a ₂ are the coefficients of a polynomial of the second degree approximating the experimentally measured dependence of OSNR on BER in the test line, when the communication line is put into operation on its site before FEC error correction is measured the value of the error coefficient BER1, during operation of the communication line on its section to and FEC error references periodically measure the average value of the error coefficient BER2 and from the value of the measured values calculate the osnr _M margin according to OSNR according to the formula:

optimally average BER2 values for at least 10 minutes.

The invention is illustrated by images, where:

in FIG. 1 - a diagram of a communication line that implements the claimed method;

in FIG. 2 - a graph of the dependence of BER to FEC on OSNR in the configuration back-to-back.

The positions shown in FIG. 1, indicate the following components of the communication line:

1 - transponder;

2 - multiplexer;

3 - demultiplexer;

4 - amplifier;

5 - fiber;

6 - source of noise radiation (noise source);

7 - attenuator;

8 - OSA;

9 - attenuator splitter;

10 - OSA splitter;

11 - signal path in the configuration Back-To-Back;

12 - span of the communication line;

The invention is based on the fact that in coherent communication systems it has been experimentally established that there is a relationship between the error coefficient (BER) before error correction and the optical ratio of signal power to total noise power (OSNR _TOT ), which can be represented as a polynomial of the second degree: OSNR _TOT = a ₀ + a ₁ log (BER) + a ₂ (log (BER)) ² , where a ₀ and ₁ and a ₂ are coefficients of a polynomial of the second degree. The coefficients of the polynomial of the second degree included in the above formula are unique for each transponder and do not change during the operation of the communication line.

The dependence of OSNR _TOT on BER is constant if and only if all noise sources in the communication system are correctly taken into account. In modern coherent communication systems, two noise sources must be considered: amplified spontaneous emission noise (ASE noise) and non-linear interference noise (NLI noise) [N.V. Gurkin, O.E. Naniy A.G. Novikov, S.O. Plaksin, V.N. Treschikov, R.R. Ubaidullaev. Nonlinear interference noise in 100 Gbit / s communication systems with DP-QPSK modulation format // Quantum Electronics, Volume 43, no. 6, pp. 550-553 (2013)]. Using an optical spectrum analyzer (OSA), only the ASE noise power level and, consequently, the OSNR _ASE value can be measured. The NLI power level and, accordingly, the OSNR _{NLI value of} noise cannot be directly measured, but it can be calculated from the OSNR _ASE values and the BER value measured at the same time if the dependence of OSNR _TOT on BER is known [N.V. Gurkin, O.E. Naniy A.G. Novikov, S.O. Plaksin, V.N. Treschikov, R.R. Ubaidullaev. Nonlinear interference noise in 100 Gbit / s communication systems with DP-QPSK modulation format // Quantum Electronics, Volume 43, no. 6, pp. 550-553 (2013)].

The dependence of OSNR _TOT on BER when measuring in a short line (Back-to-Back) coincides with the experimentally measured dependence of OSNR _ASE on BER, because NLI noise in such a line is absent. Therefore, before putting the line into operation in the laboratory, the dependence of OSNR _ASE on BER is measured in the Back-To-Back configuration. The amount of noise changes with a variable attenuator. For each position of the variable attenuator control, two values are read: OSNR _ASE and BER. The OSNR _ASE value is read from the OSA screen. The BER value is read from the computer screen through the transponder control system. Note that the BER measurement function (BER to FEC) is implemented in all coherent transponders and is measured continuously during the operation of the communication line. The resulting pair of numbers is entered in the table. Thus, a table is formed, and a graph is constructed that is used to calculate the coefficients of the polynomial a ₀ , a ₁ and a ₂ . For example, such calculations can be performed using the Excel program, which builds a graph using the points in the table and, when you select the appropriate option, also builds an approximating curve in the form of a polynomial of the second degree and calculates the coefficients of the approximating polynomial a ₀ , a ₁ and a ₂ . At the same time, the critical value of OSNR is measured when the power of the added noise is increased to a value at which the communication line stops working. This value the critical value OSNR (OSNR _BTB ) is read from the OSA screen and is an inherent characteristic of the transponder.

When putting the line into operation, we use OSA to determine the critical value OSNR (OSNR _OSA1 ) and enter it into the transponder control system. At the same time, the corresponding OSNR _OSA1 value BER1 is measured in the transponder. From the measured OSNR _OSA1 values, the BER1 and OSNR _BTB values determine the OSNR _{NLI value of} noise, which is necessary to determine the OSNR margin in the active line using only one continuously monitored parameter - BER (this BER value is denoted by BER2).

Further, when the communication line is operated every 10 minutes, the transponder determines the BER2 value by averaging the BER value over a 10-minute interval and calculates OSNR _M according to the formula:

(In the description, the osnr notation with different indices refers to the signal-to-noise ratio expressed in dB, and the OSNR notation with different indices refers to the signal-to-noise ratio expressed in relative units.)

Implementation example.

The claimed method for measuring OSNR margin in a communication line with DWDM spectral multiplexing and FEC error correction signal coding was experimentally implemented and tested on an experimental model of the communication line.

We experimentally studied the transmission of an information signal in DP QPSK format with a transmission rate of useful information of 100 Gbit / s. Given 15% redundancy of the FEC error-correcting code and 5% service information, the total bit rate is 120 Gbit / s. The experiment used a transponder 1 "Volga" manufactured by T8 with an optical module made in compact design (CFP).

In a short line, the calibration curve of the CFP module was taken (BER to FEC versus OSNR in the back-to-back configuration) shown in FIG. 2.

The measurement procedure in the back-to-back circuit is shown in FIG. 1, the variant with the short line shown by the dotted line 11. As the noise source 6, we used the EAU-100P / 2 erbium super-luminescent radiation source, the noise power is controlled by the attenuator 7. For each position of the variable attenuator regulator, two OSNR and BER values are read. The OSNR value is read from the OSA 8 screen. Anritsu MS9740A model was used in the experiment. The BER value is read from the computer screen through the T8 Fractal control system. The measurement results are entered into the Excel table; according to the data of this table, using the Excel program, the graph shown in FIG. 2, and the coefficients of the approximating polynomial a ₀ , a ₁ and a ₂ are calculated: a ₀ = 6.8, a ₁ = -4.2, and ₂ = -0.2

The critical OSNR (OSNR _BTB ) value is 13.3 dB.

At the second stage of the experiment, a model of a communication line was assembled from nine spans of 12 over 100 km with a total length of 900 km. For the optimal value of the input powers introduced into the spans, the OSNR value _{OSA1 was} measured using OSA, the value of which turned out to be 24.1 dB, while the value of BER1 turned out to be 1.05⋅10 ^-5 .

The OSNR margin measured under the same conditions, according to the standard methodology used by telecom operators, gave a value of 11.3 dB.

Calculation according to the calculation formula of the present invention gives a value of 11 dB.

The difference between the direct experiment and the calculation according to the patented method was 0.3 dB (less than 0.5 dB).

At the third stage of the experiment, the communication line worked continuously for 9 days and once every 3 days the BER2 value was measured by averaging the BER value over a 10-minute interval and calculates OSNR _M according to the calculation formula of the present invention.

The results are shown in the table.

Thus, the proposed method provides a measurement of OSNR margin in continuous mode during operation of the communication line without interrupting its operation.

The accuracy of determination of OSNR _M in the proposed method fits into 0.5 dB, which, at a minimum, is not worse than in the prototype.

Thus, we can conclude that the task is to create a simple and reliable way to measure OSNR margin in the communication line with spectral multiplexing, which does not require disconnecting the information signal from the consumer during the measurements, and the claimed technical result is simplification of the stock measurement on OSNR in the communication line with spectral multiplexing due to the possibility of continuous monitoring of the quality of work of all DWDM channels of the communication system directly during operation without interruption for the duration of Measurement measurements.

Analysis of the claimed technical solution for compliance with the conditions of patentability showed that the characteristics indicated in the formula are essential and interconnected with the formation of a stable population unknown at the priority date from the prior art and sufficient to obtain the required synergistic (super-total) technical result.

The properties regulated in the claimed method by individual features are well known in the art and require no further explanation.

The above information indicates the following conditions are met when using the claimed technical solution:

- the object embodying the claimed technical solution, when implemented, relates to the field of fiber optic communication, in particular to the evaluation of efficiency in fiber optic communication lines, and more particularly to the procedure for measuring OSNR margin in a communication line with DWDM spectral multiplexing and FEC error correction signal coding ;

- for the claimed object in the form described in the claims, the possibility of its implementation using the above-described in the application materials known from the prior art on the priority date of the means and methods is confirmed;

- the object embodying the claimed technical solution, when implemented, is able to ensure the achievement of the technical result perceived by the applicant.

Therefore, the claimed subject matter meets the patentability conditions of “novelty”, “inventive step” and “industrial applicability” under applicable law.

Claims (5)

1. A method for measuring OSNR margin in a communication line with DWDM spectral multiplexing and FEC error correction coding, which includes the following steps: before commissioning the communication line, the OSNR _BTB value and the OSNR dependence on BER are measured in the circuit with a test short line without correction FEC errors, during the commissioning of the communication line, the OSNR _OSA1 value is measured at the end of the communication line, during operation periodically measure the parameters of the communication line, the value of which, taking into account the values of the parameters measured before delivery If the communication lines are in operation, they calculate the osnr _M stock according to OSNR, characterized in that the dependence of OSNR on BER is represented as a polynomial of the second degree:

where and ₀ , a ₁ and a ₂ are the coefficients of a polynomial of the second degree approximating the experimentally measured dependence of OSNR on BER in a test line; when a communication line is put into operation on its site before error correction FEC, the error coefficient BER1 is measured, while the communication line is operating on its area, before correction of FEC errors, the average value of the error coefficient BER2 is periodically measured and the stock osnr _{M is} calculated according to the value of the measured values by OSNR according to the formula:

2. A method for measuring OSNR margin in a communication line with DWDM according to claim 1, characterized in that the BER2 value is averaged for at least 10 minutes.

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